1Converting old watchdog drivers to the watchdog framework
2by Wolfram Sang <w.sang@pengutronix.de>
3=========================================================
4 5Before the watchdog framework came into the kernel, every driver had to
6implement the API on its own. Now, as the framework factored out the common
7components, those drivers can be lightened making it a user of the framework.
8This document shall guide you for this task. The necessary steps are described
9as well as things to look out for.
10 11 12Remove the file_operations struct
13---------------------------------
14 15Old drivers define their own file_operations for actions like open(), write(),
16etc... These are now handled by the framework and just call the driver when
17needed. So, in general, the 'file_operations' struct and assorted functions can
18go. Only very few driver-specific details have to be moved to other functions.
19Here is a overview of the functions and probably needed actions:
20 21- open: Everything dealing with resource management (file-open checks, magic
22 close preparations) can simply go. Device specific stuff needs to go to the
23 driver specific start-function. Note that for some drivers, the start-function
24 also serves as the ping-function. If that is the case and you need start/stop
25 to be balanced (clocks!), you are better off refactoring a separate start-function.
26 27- close: Same hints as for open apply.
28 29- write: Can simply go, all defined behaviour is taken care of by the framework,
30 i.e. ping on write and magic char ('V') handling.
31 32- ioctl: While the driver is allowed to have extensions to the IOCTL interface,
33 the most common ones are handled by the framework, supported by some assistance
34 from the driver:
35 36 WDIOC_GETSUPPORT:
37 Returns the mandatory watchdog_info struct from the driver
38 39 WDIOC_GETSTATUS:
40 Needs the status-callback defined, otherwise returns 0
41 42 WDIOC_GETBOOTSTATUS:
43 Needs the bootstatus member properly set. Make sure it is 0 if you
44 don't have further support!
45 46 WDIOC_SETOPTIONS:
47 No preparations needed
48 49 WDIOC_KEEPALIVE:
50 If wanted, options in watchdog_info need to have WDIOF_KEEPALIVEPING
51 set
52 53 WDIOC_SETTIMEOUT:
54 Options in watchdog_info need to have WDIOF_SETTIMEOUT set
55 and a set_timeout-callback has to be defined. The core will also
56 do limit-checking, if min_timeout and max_timeout in the watchdog
57 device are set. All is optional.
58 59 WDIOC_GETTIMEOUT:
60 No preparations needed
61 62 WDIOC_GETTIMELEFT:
63 It needs get_timeleft() callback to be defined. Otherwise it
64 will return EOPNOTSUPP
65 66 Other IOCTLs can be served using the ioctl-callback. Note that this is mainly
67 intended for porting old drivers; new drivers should not invent private IOCTLs.
68 Private IOCTLs are processed first. When the callback returns with
69 -ENOIOCTLCMD, the IOCTLs of the framework will be tried, too. Any other error
70 is directly given to the user.
71 72Example conversion:
73 74-static const struct file_operations s3c2410wdt_fops = {
75- .owner = THIS_MODULE,
76- .llseek = no_llseek,
77- .write = s3c2410wdt_write,
78- .unlocked_ioctl = s3c2410wdt_ioctl,
79- .open = s3c2410wdt_open,
80- .release = s3c2410wdt_release,
81-};
82 83Check the functions for device-specific stuff and keep it for later
84refactoring. The rest can go.
85 86 87Remove the miscdevice
88---------------------
89 90Since the file_operations are gone now, you can also remove the 'struct
91miscdevice'. The framework will create it on watchdog_dev_register() called by
92watchdog_register_device().
93 94-static struct miscdevice s3c2410wdt_miscdev = {
95- .minor = WATCHDOG_MINOR,
96- .name = "watchdog",
97- .fops = &s3c2410wdt_fops,
98-};
99 100 101Remove obsolete includes and defines
102------------------------------------
103 104Because of the simplifications, a few defines are probably unused now. Remove
105them. Includes can be removed, too. For example:
106 107- #include <linux/fs.h>
108- #include <linux/miscdevice.h> (if MODULE_ALIAS_MISCDEV is not used)
109- #include <linux/uaccess.h> (if no custom IOCTLs are used)
110 111 112Add the watchdog operations
113---------------------------
114 115All possible callbacks are defined in 'struct watchdog_ops'. You can find it
116explained in 'watchdog-kernel-api.txt' in this directory. start(), stop() and
117owner must be set, the rest are optional. You will easily find corresponding
118functions in the old driver. Note that you will now get a pointer to the
119watchdog_device as a parameter to these functions, so you probably have to
120change the function header. Other changes are most likely not needed, because
121here simply happens the direct hardware access. If you have device-specific
122code left from the above steps, it should be refactored into these callbacks.
123 124Here is a simple example:
125 126+static struct watchdog_ops s3c2410wdt_ops = {
127+ .owner = THIS_MODULE,
128+ .start = s3c2410wdt_start,
129+ .stop = s3c2410wdt_stop,
130+ .ping = s3c2410wdt_keepalive,
131+ .set_timeout = s3c2410wdt_set_heartbeat,
132+};
133 134A typical function-header change looks like:
135 136-static void s3c2410wdt_keepalive(void)
137+static int s3c2410wdt_keepalive(struct watchdog_device *wdd)
138 {
139...
140+
141+ return 0;
142 }
143 144...
145 146- s3c2410wdt_keepalive();
147+ s3c2410wdt_keepalive(&s3c2410_wdd);
148 149 150Add the watchdog device
151-----------------------
152 153Now we need to create a 'struct watchdog_device' and populate it with the
154necessary information for the framework. The struct is also explained in detail
155in 'watchdog-kernel-api.txt' in this directory. We pass it the mandatory
156watchdog_info struct and the newly created watchdog_ops. Often, old drivers
157have their own record-keeping for things like bootstatus and timeout using
158static variables. Those have to be converted to use the members in
159watchdog_device. Note that the timeout values are unsigned int. Some drivers
160use signed int, so this has to be converted, too.
161 162Here is a simple example for a watchdog device:
163 164+static struct watchdog_device s3c2410_wdd = {
165+ .info = &s3c2410_wdt_ident,
166+ .ops = &s3c2410wdt_ops,
167+};
168 169 170Handle the 'nowayout' feature
171-----------------------------
172 173A few drivers use nowayout statically, i.e. there is no module parameter for it
174and only CONFIG_WATCHDOG_NOWAYOUT determines if the feature is going to be
175used. This needs to be converted by initializing the status variable of the
176watchdog_device like this:
177 178 .status = WATCHDOG_NOWAYOUT_INIT_STATUS,
179 180Most drivers, however, also allow runtime configuration of nowayout, usually
181by adding a module parameter. The conversion for this would be something like:
182 183 watchdog_set_nowayout(&s3c2410_wdd, nowayout);
184 185The module parameter itself needs to stay, everything else related to nowayout
186can go, though. This will likely be some code in open(), close() or write().
187 188 189Register the watchdog device
190----------------------------
191 192Replace misc_register(&miscdev) with watchdog_register_device(&watchdog_dev).
193Make sure the return value gets checked and the error message, if present,
194still fits. Also convert the unregister case.
195 196- ret = misc_register(&s3c2410wdt_miscdev);
197+ ret = watchdog_register_device(&s3c2410_wdd);
198 199...
200 201- misc_deregister(&s3c2410wdt_miscdev);
202+ watchdog_unregister_device(&s3c2410_wdd);
203 204 205Update the Kconfig-entry
206------------------------
207 208The entry for the driver now needs to select WATCHDOG_CORE:
209 210+ select WATCHDOG_CORE
211 212 213Create a patch and send it to upstream
214--------------------------------------
215 216Make sure you understood Documentation/SubmittingPatches and send your patch to
217linux-watchdog@vger.kernel.org. We are looking forward to it :)
218 219